1. Field of the Invention
The present invention relates generally to a semiconductor image sensor device and, more particularly, to a front-side illuminated (FSI) CMOS image sensor (CIS) device having an in-substrate reflective cavity structure and a fabrication method thereof.
2. Description of the Prior Art
Complementary metal oxide semiconductor (CMOS) image sensor has been widely used in, for example, security monitoring, digital cameras, toys, cell phones, video phones and other imaging products. With smart phones and tablet PCs become thinner, lighter, and more complicate, CMOS image sensor needs to continue to reduce the size and improve the resolution.
Generally, a CMOS image sensor comprises a plurality of pixels arranged in a pixel array. Each pixel typically has a photodiode fabricated within a semiconductor substrate. The incident light can be converted to a current signal.
As the size of the CMOS image sensor continues to shrink, the spacing between two adjacent pixels also decreases. The incident light causes increased optical scattering noise between the pixels, leading to reduced quantum efficiency (QE) and photosensitivity. The decreased spacing between two adjacent pixels also results in severe optical crosstalk. The aforesaid optical interference makes the spatial resolution and the overall sensitivity of the image sensor difficult to improve, and will produce color mixing, which causes the image noise.
Therefore, there remains a need in the art for an improved CMOS image sensor structure, which is capable of solving the problem and the drawback of the prior art, in particular, to improve the optical crosstalk between pixels, and improve the quantum efficiency.